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hey ampeggers! pickup this thread for a ride!

Discussion in 'Amps and Cabs [BG]' started by basstark, Sep 16, 2004.

  1. basstark


    Jun 6, 2004
    hey yall. i'm in the market for a vintage svt buts i gots me a question i was hoping yall could answer. the sound difference between pre magnavox era and magnavox era. reading the threads, i find that the 69 heads used a rarer power tube section. but is it true that pre magnavox were made with 6550's in 1970? also and again what do some of you folk think about the comparison in sound, parts and maintanance between the pre and magnavox era. not much conclusive on the threads so maybe this one will provide us all with some more insight. also thanks to all yall for the other info i picked up searching through threads. theres a party at talkbass now and everyones invited! thanks for help!
  2. notanaggie

    notanaggie Guest

    Sep 30, 2003
    Pre-6550 used a 6146 radio power tube. While you can still get those, sometimes, there isn't any point to it.

    The 6550 is about 1/3 the cost these days, or less.

    They put out a mod for the 6550 to convert the 6146 unit to 6550. I would be surprised if many hadn't had that done sometime in the last 34 years.
  3. basstark


    Jun 6, 2004
    cool. part of what im wondering is if there are any pre magnavox svt's that were made with the 6550. and thus, if one has 6550s, does that mean it has been modded?
  4. basstark


    Jun 6, 2004
    COME AMPEGGERS ANSWER MY QUESTIONS! I know someones got to answer or refer someone else to this thread! thanks yall
  5. Yes. They only did the first year with 6146s. They used 6550s after 1969. Any Ampeg that says 'The Ampeg Company, Linden NJ' on the back is pre-Magnavox. Psycho Bass Guy is the guy who knows the Ampeg history best on this board, I'm sure he'll post on it eventually (and correct me if I'm wrong :D).
  6. basstark


    Jun 6, 2004
    thanks for the post. im looking around for an old svt and i was figuring it would probly be best with the easier access 6550's. what do yall think about the sound difference with 6550's and 6146's? and are there other differences in make and design between either 1969 heads and after or the linden and magnavox in general? i read that in about 1980 they started in with the cheaper transformers and who knows what else. any info yall! and anyone looking to sell vintage svt! im at sscotark@aol.com!
  7. My V4 says Ampeg,Magnavox, Linden, NJ on the schematic.
  8. basstark


    Jun 6, 2004
    if anyone thinks another has a comment on the quality differences of the pre magnavox and the magnavox svt refer them to this thread if it aint too much trouble. thanks for all so far!--steve
  9. "pre Magnavox" is tricky terminolgy. That's because there were other companies like Selmer/Univox that owned Ampeg before Magnavox and after the 6146b was dropped. So what you're getting at might be more clearly thought of as the SVTs designed with 6550 tubes vs. 6146b's. Those just happen to be the very first ones that were built in '69 and possibly early '70 while "The Ampeg Co. of Linden, NJ" was for the most part still owned by the original guys. (FWIW, the vast majority of threads here regarding SVT tonal differences are aimed at SLM vs. Pre-SLM SVTs if anything.)

    As for the differences between 6550 vs. 6146b in an SVT I can tell you that the 6550 is da bomb! I can tell you that the one 6146b that I have heard is da bomb also even though it was a real beater which had only been abused and never given any love. It still sounded silky, silky good. Every bit as good as the 6550 design, IMO.

    Out of an amp, spec-wise I can not offer much help. The practical advice given me is that 6146b tubes are scarce and expensive. Also that the 6550 is more robust and more suited to the SVT than the 6146b.
  10. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    A little history of design changes...

    At the end of Magnavox production of SVT, there was a change to eliminate the 12DW7 in the preamp. The 12DW7 is a mix, with one 12AX7 high gain section, and one 12AU7 low gain section. It was getting hard to find at decent quality.

    The change substituted 12AX7 for the 12DW7, effectively changing several tube stages from a low gain to a high gain tube. There is a sound change from this. The change persisted through MTI to SLM.

    After Magnavox, MTI made Ampegs (sort of). They moved production to Japan, and the transfomers were made over there also. Those output transformers don't sound as good, in our opinion. That may be the origin of the 1980 date for cheaper transformers. But that was ONLY MTI.

    The SLM original was made as close as possible to the last Magnavox production. We went BACK to the US transformer maker (in Chicago) and actually some of the folks there who had worked on them for Magnavox were still there at the time, so we are pretty certain they are made right. They better be, for what they cost....Despite pleas from purchasing, we have yet to find any cheaper unit that sounds right, so we still use that vendor, although they have been sold off and are now part of a conglomerate of some sort.

    Those units, and later ones, have the 12AX7 for 12DW7 substitution. If you have 12DW7s, the mod can be un-modded back to original.
    The other change was substituting for the 12BH7 in the power amplifier. That has been argued over, as far as drive capability, etc, and I don't want to get that going again. They may sound different, since it is a change, but I don't agree that the reason is that the drive is too little....'nuff said.

    Various SVT derivatives have had various versions of the preamp since, and there have been bias lights and various protection schemes put in place at various times since 1986. A list of all would be too involved for this thread.

    However, the power amp has remained basically constant, and the same vendor still makes the output transformer that made them for Magnavox. The power transformer has had a couple vendors, it isn't as "magic".

    More recent SVT derivatives, the first being the SVP-CL, have returned to the pre-12DW7 mod preamp, using 12AU7 tubes in place of the low-gain portions and the old 6C4 output follower. I made plenty of noise until that was done, and the result seems to be worth it.

    There is always an argument about sound whenever a change is made in a "classic" unit. "Before" is usually stated to be "better".

    It is certainly "safe" to say that the "classic" version is not "worse" than a new version, or it wouldn't be "classic", it would just be "old". So the "old is better" may be an informed opinion, by someone who can tell the difference, or it may be someone who doesn't know just parroting a "safe" opinion. There is a lot of that.

    You kind of have to be the judge. If you don't notice the difference, after playing both, then it may not be important to you. For another person, a sound detail may be obviously different, and it may be the key issue deciding their "purchase decision".
  11. I have a very early '69 that I'm in the process of restoring. The date codes on the transformers indicate they were made in May, 1969. Mine also has a chrome-plated chassis - not black as virtually every other SVT I've seen has. There's no silk-screening on the back of the chassis; rather, there's an aluminum strip that screws on top of it that has the screening on it. It also has the socket for the Amperite delay tube.

    All that said, from all indications (pot date codes, black switches, etc.) the preamp is from a '74. I have no idea when or why this change was made.

    I'm presently recapping it and hope to have it running again soon.

    -- busmandan --
  12. What kind of output tubes does yours have? Can you post pics?
  13. It was completely stripped of tubes when I got it; however, I know it originally had 6146's since the chassis has the grommets for the plate caps.

    I have pictures posted here .

    -- busmandan --
  14. Whoa Bessie! What da heck's that? A prototype? Wow! Where's PBG? He'll know (pressure).

    What do you know about that socket on the left? Is that AC? Do I see only two prongs for it or three? Can you ID everything left to right?

    Texas Alternative Blues Rock? The more I think about that the bigger my smile gets.

  15. We talked about that amp on the Dudepit. It appears to be parted togther comglomeration, whether a tech or the factory did it, nobody's sure, although I doubt anyone at Magnavox would have taken the time to do that. I'm guessing it's a repair/cannibalism thing. EARLY- EARLY SVT's used a relay tube instead of a standby switch. That's what the socket is for.

    BTW, 6146's are basically 6550's with a top plate cap anyway. They can't take as much grid voltage (hence the sometimes there, sometimes not grid clamping diodes in different era SVT's) and don't produce as much power, so they overdrive a LITTLE easier, but they basically sound the same. ANY pre-SLM SVT is going to sound pretty similar to the "ideal SVT tone", and there are a lot of stories about the amp that are just outright false, but so many people repeat them, they get taken as truth. The biggest consistent differences I've seen have only been in internal wire gauges and board layout. For as long as that amp stayed in production, the last ones made that were not reissues were STILL virtually identical to the first steadily produced ones.
  16. Quick note here: EVERY old SVT (at least that I've seen) has the aluminum strip for the back.
  17. The socket you speak of is the AC power. And yes, it has two male spades on it. I suppose the idea was to use an everyday extension cord to run power on those arena stages!

    I'll give you the ID's on everything later.

    Regarding Texas Alternative Blues Rock - when your band and songs don't clearly fit in an existing catagory, it's perfectly acceptable to create your own - right?

    -- busmandan --
  18. Hmmm. I guess that you didn't read PBGs authoritative response to the question.

    Anyhow, if I'm not mistaken the socket in question is the tube socket on top next to the molex connector.

  19. Actually, the socket KOA is referring to is in a different picture - one of the back of the chassis. The "socket" on the far left is where someone has hacked the power cord out and replaced it with a cup that has two Edison spades on it.

    The socket next to the Molex connector is for an Amperite delay tube.

    -- busmandan --
  20. Right. I was referring to a different pic that was more of a rear view. In the back of my mind I was thinking it could be a retrofitted DI of sorts.

    I saw an SVT ('76ish) on Ebay that had an added DI.